3GPP (The 3rd Generation Partner Project) standardization organization is working out the next generation of wireless communication standard which is named LTE (Long Term Evolution). In a physical layer interface, the new standard adopts OFDM (Orthogonal Frequency Division Multiplexing) technology, which is different from conventional CDMA (Code Division Multiple Access) technology. In LTE, OFDMA (Orthogonal Frequency Division Multiple Access) is used in downlinks (DL) and SC-FDMA (Single Carrier Frequency Division Multiple Access) is used in uplinks (UL). The technology used in the new standard is effective for multi-path propagation, with adoption of frequency domain equalization reducing complexity of the conventional time domain equalization, and is more suitable for wider bandwidth high-speed data transmission.
The 3GPP is also working out LTE-Advanced (Advanced-LTE) which is likely the major enhancements to LTE. The LTE-Advanced will be introduced in Release 10 after a correction and improvement phase in LTE Release 9. LTE-Advanced shall fulfill the requirements as set by the ITU (International Telecommunication Union).
In LTE-Advanced, the size of UCI (Uplink Control Information, e.g., HARQ-ACK/NACK, CQI (Channel Quality Indicator), PMI (Precoding Matrix Indicator, for example, indicated by 2 kinds of channel properties, W—1: taking care of wideband and/or long-term channel properties, W—2: matching the instantaneous properties of the effective channel), RI (Rank indication)) will increase rapidly, e.g., due to downlink cooperative multipoint (CoMP) transmissions, carrier aggregation, and/or higher order MIMO.
Carrier aggregation, where two or more component carriers are aggregated is considered for LTE-Advanced in order to support transmission bandwidth larger than 20 MHz, up to 100 MHz (see Non-Patent Document 1 below). From a UE perspective, there is one transport block (in absence of spatial multiplexing) and one HARQ entity per scheduled component carrier. A UE may be scheduled over multiple component carriers and each transport block is mapped within a single component carrier.
According to current assumption of LTE-Advanced, the uplink multiple access has the following properties (see Non-Patent Document 2 below). Multiple transmission antennas will be used for LTE-Advanced uplink transmission and DFT (Discrete Fourier transform)-precoded OFDM is the transmission scheme used for PUSCH (Physical Uplink Shared Channel) both in absence and presence of spatial multiplexing. In case of multiple component carriers, there is one DFT per component carrier. Both frequency-contiguous and frequency-non-contiguous resource allocation is supported on each component carrier. Simultaneous transmission of uplink L1/L2 control signaling and data (e.g., UL-SCH (Uplink Shared Channel) transport blocks, UL-SCH (Uplink Shared Channel) data) is supported through two mechanisms: control signaling is multiplexed with data on PUSCH according to the same principle as in Rel-8; control signaling is transmitted on PUCCH (Physical Uplink Control Channel) simultaneously with data on PUSCH.
Regarding UCI (Uplink Control Information) multiplexing on PUSCH, some contributions propose how to deal with the UCI transmission on multiple layers of multiple codewords (see Non-patent Document 3). The design of multiplexing of UCI and data on PUSCH for multiple transmission antennas UEs must take some aspects into consideration that were not an issue in the single antenna PUSCH transmission of LTE Rel-8. For example, UCI is mapped onto all the 4 layers, or is mapped onto 2 layers of one selected codeword, or is mapped onto a single layer of one selected codeword. All these techniques just focus on the physical layer processing and they do not involve any scheduling and channel coding related procedure.
Non-Patent Document 1: “Carrier aggregation in LTE-Advanced”, 3GPP TSG RAN WG1 Meeting #53bis, R1-082468, June, 2008.
Non-Patent Document 2: “3GPP TSG RAN Further Advancements for E-UTRA Physical Layer Aspects (Release 9)”, 3GPP TS 36.814 V2.0.1, 2010-03.
Non-Patent Document 3: “Further Discussion on Data and Control Multiplexing in UL MIMO Transmissions”, 3GPP TSG RAN WG1 Meeting #61, R1-103037, May, 2010.